This invention relates to methods of and apparatus for liquid chromatography, in particular high-pressure liquid chromatography (HPLC), sometimes known as high-performance or high-speed liquid chromatography, though also applicable to traditional liquid chromatography.
In HPLC, a solution containing one or more constituents is forced rapidly through a chromatographic column. The retention volume (in practice the time at constant flow-rate) after which a constituent arrives at the column output in the eluent is characteristic of the constituent. Known techniques for detecting this arrival include measuring optical absorption (using UV or visible light), fluorescence, refractive index or electrochemical behaviour, eg electro-oxidation or -reduction potential.
Some substances are inherently suitable for such detection but others may not possess a suitable detectable property. For example they may not fluoresce at all, or not to a degree or at a wavelength which gives the required degree of selectivity or sensitivity. Some substances can, however, be modified photochemically by irradiation with light of a suitable wavelength, and the present invention utilises this fact to enable substances otherwise unsuitable for detection by HPLC to be detected thereby. Examples of such substances are cannabinoids, whose detection in body fluids is of forensic importance; Bowd et al have shown (Talanta, 1971, pp 697-705) that cannabis has constituents, for example CBN )(cannabinol), which can be modified photochemically by irradiation with UV to yield a substance with an enhanced UV fluorescence at a wavelength suitable for detection.